For many years conventional magnetic storage devices have been used to store data and information. Magnetic storage devices generally include a magnetic medium with units (e.g., bits) of magnetic material that can be polarized to distinct magnetic states. The direction of the magnetization points in different directions, which can be referred to as a positive state and a negative state. Each bit can store information (generally binary information in the form of either a 1 or a 0) according to the magnetic polarization state of the bit. Accordingly, magnetic storage devices generally include a “read” element that passes over the magnetic material and perceives the magnetic polarization state of each bit and a “write” element that passes over the magnetic material and changes the magnetic polarization state of each bit, thereby recording individual units of information. Therefore, the amount of information that can be stored on a magnetic storage medium is proportional to the number of magnetic bits on the magnetic storage medium.
There are various types of magnetic storage media and each type involves different fabrication techniques. For example, conventional granular magnetic recording media are disks that have multiple grains in each magnetic bit. In granular magnetic media, all of the domains are co-planar and the surface of the disk is relatively continuous. In order to increase the amount of information that can be stored on a granular magnetic disk, the number of grains per magnetic bit can be decreased while keeping the grain size approximately the same. However, with fewer grains in each bit, there is decreased signal-to-noise ratio (e.g., less signal and more noise). In order to maintain a better signal to noise ratio, methods have been developed that decrease both the size of the magnetic bit and the size of the individual grains making up each magnetic bit, thus keeping the same number of grains in each magnetic bit. However, when the grains become too small, thermal fluctuations can cause the grains to spontaneously reverse polarity, thus resulting in unstable storage and a loss of information.
Bit-patterned media is another example of magnetic storage media. In bit-patterned media, each bit is a single magnetic domain rather than a collection of contiguous magnetic grains. The bits can be topographically patterned using lithographic and etching techniques to form magnetically isolated bit islands surrounded by trenches. In some instances, the trenches are formed by etching away a magnetic material. In yet other instances, the physical patterns are etched into a non-magnetic substrate and then a magnetic material is coated over the patterned substrate. Because of the physical separation between the elevated bit islands and the trenches, the width of each distinct bit island can be decreased in order to increase the areal bit density of the device, while still maintaining a high signal-to-noise ratio and high thermal stability.
However, because bit-patterned media is topographically patterned, a planarization process is often required in order to fill in the trenches with a magnetically inert material to create a smooth surface over which the read/write head may pass. As areal bid density increases, read/write heads must fly closer to the magnetic surface in order to sense and record magnetic polarization states. If bit-patterned media were not planarized, the uneven surface of a medium would cause read/write heads to turbulently fly across the surface of the medium and crash into the medium, likely causing catastrophic data loss and device failure.
In conventional granular magnetic media (non bit-patterned), carbon overcoat layers are often used to protect the magnet medium. Overcoat layers containing carbon beneficially improve corrosion resistance, enhance the tribological properties of the medium, and bond well with the polymer lubricants used in magnetic hard drive applications. However, when a conventional carbon overcoat layer is used as the inert filler material in a bit-patterned media application, conventional planarization techniques, such as chemical-mechanical polishing, are not efficiently able to polish the conventional carbon containing filler layer, if at all. Thus, in order to planarize and protect bit-patterned media, multiple processing steps using various materials are often required, thereby adding to the complexity and expense of media fabrication.